1. Field of the Invention
The present invention relates to a resolver signal processing method and apparatus for obtaining data value (for example, rotation torque or rotation angle) relating to rotation inputted into these plural resolvers by arithmetic operation based on resolver signals outputted from plural resolvers having a different number of counter electrodes.
2. Description of the Related Art
Conventionally, as a means for detecting a rotation torque or a rotation angle using plural (for example, two) resolvers having a different number of counter electrodes, an absolute position detecting apparatus disclosed in a following patent document 1 has been well known. In the absolute position detecting apparatus of this patent document 1, an input shaft and an output shaft are connected to each other through a torsion bar so as to detect a rotation angle of the input shaft by a first resolver and a rotation angle of the output shaft by a second resolver. Consequently, a rotation torque is computed based on the spring coefficient of the torsion bar which is twisted when both the shafts rotate relative to each other and a difference of the rotation angle between the both shafts, so as to achieve a torque sensor.
According to the prior art, the absolute position detecting apparatus capable of computing the absolute position (steering angle) of a handle to be inputted into a second resolver by using a deflection in cycle of the detection signals of both the resolvers is constituted of the second resolver capable of detecting a rotation angle of the output shaft and a motor resolver capable of detecting a rotation angle of an electric motor for generating an assist force for an electrically-powered steering. In the meantime, the rotation angle of an input shaft can be detected within a range of 360° by the first resolver and the second resolver.
Prior Art: JP 2003-75109 A is incorporated herein by reference.
In case of detecting a rotation torque and a rotation angle using plural resolvers each having a different counter electrode number, a reference value for computation is obtained from an outputted resolver signal by providing the resolver with a known rotation input serving as a reference and the rotation torque and the rotation angle are obtained by computation based on that reference value. Thus, as described later, a rotation input exceeding that range cannot acquire an appropriate computed value due to a limitation of the allowable input range, which is generated by a combination of plural resolvers each having a different counter electrode number.
More specifically, if in an electrically-powered steering, its torque sensor is constituted of for example, two resolvers each having a counter electrode number of 5 and a counter electrode number of 6, an input torque (steering torque) by the steering wheel is computed based on resolver signals outputted from these resolvers. In this case, as shown in FIG. 14, the input torque is computed based on a zero point (hereinafter referred to as real zero point) α which takes the input torque zero point of the steering wheel as a reference. Then, because when the resolvers each having the counter electrode number of 5 and the counter electrode number of 6 are combined, the input angle difference of both the resolvers is limited within a range of ±6° for the reason described later, if the torsion bar is twisted over this range, no appropriate output torque can be obtained by computation (inside of a dashed line ellipse in FIG. 14). Although usually, a rotation input exceeding this allowable input range is often restricted by a mechanical component such as a stopper mechanism, it is difficult to say that there is no possibility that the rotation input exceeding the allowable input range may occur due to a limit in the installation accuracy of each system component such as a resolver and torsion bar or a damage of the stopper mechanism.
Further, the installation accuracy of each system component is demanded strictly for the necessity of obeying the limitation of the allowable input range and securing as large a range of an actually measurable input torque as possible. Thus, the limitation of the allowable input range obstructs relaxing of the installation accuracy and makes it difficult to reduce installation cost. The reason why a flat portion exists on both ends of an input torque in the characteristic graph of the output torque to the input torque shown in FIG. 14 is that the rotation input is suppressed by the stopper mechanism in this range and the dotted line indicates an example of an output torque when no stopper mechanism is provided.
As shown in FIG. 15, it is considered that these problems can occur if the rotation angle sensor is constituted of plural resolvers. That is, when the resolvers each having the counter electrode number of 5 and the counter electrode number of 6 are combined, the input angle difference of both the resolvers is limited to the range of ±6° for the reason described later like the torque sensor described previously. Consequently, when the torsion bar is twisted over this range, no appropriate output torque can be obtained by computation (inside of a dashed line ellipse in FIG. 15).